Just seen on BBC4 a film called 'Under Night Streets' about the people who maintained the LU system in the 4hrs it got shut down each night, amongst things seen, cleaning the ventilator and escalator shafts, scheduled track replacement and dealing with a broken rail (with only just over an hour before trains start running again...). If you didn't see it look out for any repeat - the film is only 20 mins long but highly interesting to see how they did things, the working conditions, and not to mention a few glimpses late '50's London streets and LU stock.